This invention relates to a microdevice enclosed in an evacuated cavity.
Deposition techniques for thin layers used in semiconductor and MEMS devices often have gases incorporated in the layers during deposition. These devices may then be encapsulated in an evacuated cavity for proper functioning. However, the gases incorporated in the films may escape from the layers during the devices' lifetimes, raising the pressure in the evacuated cavities. Accordingly, many designs include a “getter” material, a reactive, generally metal layer, whose purpose is to absorb these gases, and maintain the vacuum levels within the package. Because of the reactive nature of these materials, they also tend to oxidize at the surface, forming an oxide layer that must be removed in order to activate the getter.
Current packaging techniques for vacuum-encapsulated packages require high temperatures, in excess of 400 degrees Centigrade to activate the getters. At this temperature, the oxide layers are generally driven into the bulk of the getter material, leaving the surface relatively clean and able to absorb additional impurity gases. These temperatures are consistent with those required to fuse glass frit, which is often used for vacuum encapsulation, because the melting temperatures simultaneously fire, or activate, the getter.
However, these high temperatures are incompatible with many of the materials and structures included in these devices, which cannot withstand these temperatures without melting or evaporating. Thus, the encapsulation of many small, delicate devices in a sealed vacuum cavity remains an unresolved problem, because there is presently no way to activate the getter without exposing the devices to high (>400 C) temperatures.